The present invention relates to image display apparatus in which high resolution images are displayed by shifting pixels based on an optical wobbling operation.
It is known in image display apparatus using a liquid crystal display device or the like to improve resolution of the liquid crystal display device by performing a pixel shifting operation called xe2x80x9cwobblingxe2x80x9d where the optical axis of light from the liquid crystal display device is wobbled in predetermined directions.
A technique for improving resolution has been disclosed, for example, in Japanese patent application laid open No. 4-63332, in which two sets each consisting of a liquid crystal panel for controlling the direction of polarization and a quartz plate are used for a displaying liquid crystal panel and at the same time four frame memories are employed therefor. A 4-point pixel shift is effected by causing an image to shift horizontally by xc2xd pixel pitch through one set of the polarizing direction control liquid crystal panel and quartz plate and causing the image to shift vertically by xc2xd pixel pitch through the other set of polarizing direction control liquid crystal panel and quartz plate. In other words, one frame is composed of four fields with dividing image signals into four images, and each divided image is stored to a frame memory. These are then synthesized as displayed at respective positions by allowing a straight propagation through the two sets of liquid crystal panels for a first filed, by shifting horizontally by xc2xd pixel pitch for a second field, by shifting vertically by xc2xd pixel pitch for a third field, and by shifting xc2xd pixel pitch both horizontally and vertically for a fourth field. A high-definition image based on the 4-point pixel shift is thereby displayed.
Further, a disclosure has been made in Japanese patent application laid open No. 7-36054 with respect to an optical apparatus achieving high resolution by two-dimensional 4-point pixel shift, provided with two sets of one-dimensional 2-point pixel shifting devices each consisting of a liquid crystal phase modulation device and a birefringence medium. These are combined into a lamination with rotating one of the devices about the optical axis of incidence through 90 degrees with respect to the other to perform four times of pixel shift vertically and horizontally within one frame or one field.
The prior techniques as described above are both related to performance of 4-point pixel shift to attain a quadruple resolution by shifting horizontally, vertically and obliquely by xc2xd pixel pitch the pixels of a rectangularly arrayed liquid crystal display device having horizontal pixel pitch Px and vertical pixel pitch Py.
The following problem then occurs if the above described 4-point pixel shift system is simply applied to a liquid crystal display device having pixels disposed in a delta-array of the generally used type as shown in FIG. 1, so as to perform the 4-point pixel shift as shown in FIG. 2. In particular, a frequency band diagram of FIG. 3 results when changes in frequency band are considered in the case of effecting the above described 4-point pixel shift system. Referring to FIG. 3: the transverse axis represents the frequency band in a horizontal direction; the vertical axis represents the frequency band in a vertical direction; the black small circle represents the origin (zero frequency); and white small circles represent the sampling frequencies of the liquid crystal display device. Here, from the sampling theorem where information obtained by sampling is to possess its frequency band only up to xc2xd of the sampling frequency, the original frequency band of the liquid crystal display device without performing pixel shift, as indicated by the darker dotted region xe2x80x9caxe2x80x9d, is extended to the frequency band of the lighter dotted region xe2x80x9cbxe2x80x9d upon performance of 4-point pixel shift as the above. In thus extended frequency band, as can be seen from FIG. 3, while the frequency band is increased in the vertical and oblique directions, the frequency band in the horizontal direction is not increased at all even after the performance of 4-point pixel shift, resulting in a problem that the horizontal resolution is not improved.
The present invention has been made to eliminate the above problems in the case of applying 4-point pixel shift system of the conventional liquid crystal display device to a liquid crystal display device having delta-array. It is an object of the invention to provide an image display apparatus having 4-point pixel shift system capable of increasing frequency band and improving resolution in both horizontal and vertical directions.
To solve the above problems, there is provided an image display apparatus in accordance with a first aspect of the invention, including: a display device having pixels disposed in a delta-array; pixel position transition means for repeatedly making a transition of pixel positions of the display device respectively to each of positions at four points; and image transition means for making a transition of image signals in synchronization with the pixel position transition means so as to display images corresponding to the pixel positions on the display device. The pixel positions at the four points are: a first pixel position serving as standard; a second pixel position shifted from the standard, first pixel position in a horizontal direction by approximately xc2xd of horizontal pixel pitch Px ; a third pixel position shifted from the standard, first pixel position in the horizontal direction by approximately xc2xe or approximately xc2xc of horizontal pixel pitch Px and in a vertical direction by approximately xc2xd of vertical pixel pitch Py; and a fourth pixel position shifted from the standard, first pixel position in the horizontal direction by approximately xc2xc or approximately xc2xe of horizontal pixel pitch Px and in the vertical direction by approximately xc2xd of vertical pixel pitch Py.
Of the pixel positions changed by the pixel position transition means: the third pixel position {circle around (3)} is thus determined as shown in FIG. 4 to be shifted from the first, standard pixel position {circle around (1)} horizontally by approximately xc2xe of horizontal pixel pitch Px and vertically by approximately xc2xd of vertical pixel pitch Py; and the fourth pixel position {circle around (4)} is determined to be shifted from the first, standard pixel position {circle around (1)} horizontally by approximately xc2xc of horizontal pixel pitch Px and vertically by approximately xc2xd of vertical pixel pitch Py. As shown in FIG. 6, the original frequency band of the liquid crystal display device without performing pixel shift as indicated by the darker dotted region xe2x80x9cAxe2x80x9d is thereby extended to the frequency band of region xe2x80x9cBxe2x80x9d which is lightly dotted. The frequency band is increased in both the vertical and horizontal directions. It is thereby possible to double the resolution not only in the vertical direction but also in the horizontal direction.
Further, resolution in the vertical and horizontal directions can be similarly doubled also by inverting the third pixel position {circle around (3)} and the fourth pixel position {circle around (4)} as shown in FIG. 5A, i.e., by determining the third pixel position {circle around (3)} to be the position shifted from the standard, first pixel position {circle around (1)} by approximately xc2xc of horizontal pixel pitch Px in the horizontal direction and by approximately xc2xd of vertical pixel pitch Py in the vertical direction and determining the fourth pixel position {circle around (4)} to be the position shifted from the standard, first pixel position {circle around (1)} by approximately xc2xe of horizontal pixel pitch Px in the horizontal direction and by approximately xc2xd of vertical pixel pitch Py in the vertical direction. Furthermore, as shown in FIG. 5B, a similar advantage can be obtained by inverting the direction of horizontal shift of the third and fourth pixel positions.
It should be noted that xe2x80x9cpixel pitchxe2x80x9d is defined such that pitch between the adjacent pixels is the pixel pitch in a black-and-white display device and, in the case of a color display device as shown in FIG. 7, pixel pitch of the same color in the same line is the horizontal pixel pitch Px while pitch between the lines is the vertical pixel pitch Py.
In a second aspect of the invention, the pixel position transition means in the image display apparatus according to the first aspect includes: a first pixel position transition device having a first polarization control means for switching the direction of polarization of incident light and a first optical path control means for switching optical path in accordance with the direction of polarization of emergent light from the first polarization control means; a second pixel position transition device disposed serially to the first pixel position transition device, having a second polarization control means for switching the direction of polarization of incident light and a second optical path control means for switching optical path in accordance with the direction of polarization of emergent light from the second polarization control means; and polarization rotating means disposed between the first pixel position transition device and the second pixel position transition device, for rotating the direction of polarization of incident light through a predetermined angle xcex8=tanxe2x88x921{(2Py/Px)xc2x1nxc2x7xcfx80/2}, (n=0, 1, 2, . . . ).
In a third aspect of the invention, the pixel position transition means in the image display apparatus according to the first aspect includes: a first pixel position transition device having a first polarization control means for switching the direction of polarization of incident light and a first optical path control means for switching optical path in accordance with the direction of polarization of emergent light from the first polarization control means; a second pixel position transition device disposed serially to the first pixel position transition device, having a second polarization control means for switching the direction of polarization of incident light and a second optical path control means for switching optical path in accordance with the direction of polarization of emergent light from the second polarization control means; and polarization rotating means disposed between the second polarization control means and the second optical path control means of the second pixel position transition device, for rotating the direction of polarization of incident light through a predetermined angle xcex8=tanxe2x88x921{(2Py/Px)xc2x1nxc2x7xcfx80/2}, (n=0, 1, 2, . . . ).
By using thus constructed polarization rotating means in forming the pixel position transition means, it is possible to readily set a desired oblique shift angle and hence to readily make a transition to the pixel positions at the above described four points.
In a fourth aspect of the invention, the pixel position transition means in the image display apparatus according to the first aspect includes: a first pixel, position transition device having a first polarization control means for switching the direction of polarization of incident light and a first optical path control means for switching optical path in accordance with the direction of polarization of emergent light from the first polarization control means; and a second pixel position transition device disposed serially to the first pixel position transition device, having a second polarization control means for switching the direction of polarization of incident light, a second optical path control means for switching optical path to a horizontal or vertical direction in accordance with the direction of polarization of emergent light from the second polarization control means, and a third optical path control means for switching optical path to a vertical or horizontal direction in accordance with the direction of polarization of emergent light from the second polarization control means.
By thus constructing the pixel position transition means, devices of the same type can be used to form the first polarization control means and the second polarization control means and, since an optical path control means is less expensive than a polarization rotating means, the pixel position transition means can be achieved at a lower cost.
In accordance with a fifth aspect of the invention, there is provided an image display apparatus including: a display device having methodically disposed pixels; pixel position transition means for making a transition of pixel positions of the display device respectively in an oblique direction; and image transition means for making a transition of image signals in synchronization with the pixel position transition means so as to display images corresponding to the pixel positions on the display device.
The pixel position transition means comprises:
polarization control means for switching the direction of polarization of incident light; a first optical path control means for switching optical path to a horizontal direction in accordance with the direction of polarization of incident light; and a second optical path control means for switching optical path to a vertical direction in accordance with the direction of polarization of incident light.
In thus constructed image display apparatus, pixels can be transited in an arbitrary oblique direction by changing a set value (value corresponding to thickness of birefringence plate) of the first optical path control means for horizontally shifting light polarized in horizontal direction and a set value (value corresponding to thickness of birefringence plate) of the second optical path control means for vertically shifting light polarized in vertical direction. It is therefore possible to comply with pitch in the array of any display device.